This invention relates to an apparatus for heating the contents in a relatively thin walled electrically conductive metal container such as a standard aluminum can. The device of this invention is useful, for example, for heating fluids, liquids or slurries and formed solids including foods and beverages, medicines, cosmetics, chemicals and other materials while in their metal containers.
It has been known for many years that water or other fluids can be heated with electricity.
One method of heating water or other substances in a container has been the use of a resistance heater. In such a heater, an insulated wire is submerged in the liquid. Electric current flowing through the wire heats the wire which in turn heats the liquid.
Another method that has been used, generally to heat liquids in ferromagnetic pipes such as iron or steel pipelines, is to form an alternating current electric circuit using an insulated conductor that extends a considerable distance along the inside of the pipe. In such a system, the insulated conductor constitutes one leg of the circuit and the pipe itself constitutes the return leg. Examples of such heaters are shown in U.S. Pat. Nos. 3,665,154; 3,983,360; and 3,777,117. These devices require a ferromagnetic conduit and alternating current because the heat effect is generated by magnetic hysteresis as a "skin effect" on the inner surface of the pipe as the polarity of the alternating current changes. These devices also require an insulated conductor extending a considerable length through the conduit and, therefore, need special construction to install the conductor in the pipeline.
In U.S. Pat. No. 3,975,617, it is disclosed that the "skin effect" can be used to heat a conduit without using an interior conductor wire. In that patent it is disclosed that if the insulated wire is affixed to the external surface of an iron or steel pipe, then the alternating current in the return leg through the pipe concentrates in a band on the outer surface of "skin" of the pipe close to the wire thus greatly increasing the heat produced in the pipe wall. No current is carried by the inner wall of the pipe or the part of the outer wall spaced away from the wire of conductor.
Since both of the methods utilizing the A.C. skin effect, i.e., with the conducting wire in the interior or with the conducting wire on the exterior of the conduit, require ferromagnetic conduits, they are of little value in the heating of conventional containers made of non-ferromagnetic materials such as aluminum. Another recognized disadvantage of both these methods is that electricity flows in or through the contents of the container which may produce an electrolytic effect on the contents, generating gases, and creating other similar and harmful contaminating effects.